1. Field of the Invention
The present invention relates to a condenser microphone which has a separable microphone unit including a diaphragm vibrating in response to sound waves and a fixed electrode arranged to face the diaphragm, and a body having a circuit portion for processing audio signals. More particularly, the present invention relates to a condenser microphone which can prevent problems, such as burnout of the diaphragm, from being caused when the microphone unit is removed.
2. Description of the Related Art
One condenser microphone may include, for example, two condenser microphone units, as disclosed in JP 2012-65147 A. This condenser microphone is configured to have directivity variable by adjusting a polarization voltage applied to each of the units, but such a condenser microphone is disadvantageously expensive in cost.
While, a condenser microphone is known which has a changeable microphone unit (head case) configured to be removed from a microphone body accommodating a circuit portion or the like for processing audio signals. According to this configuration, only units having different directivities need to be interchanged to readily achieve a variable directivity microphone at low cost.
FIG. 5 is a side view of the conventional condenser microphone having a removable microphone unit, and FIG. 6 is a cross-sectional view of the conventional condenser microphone. It is noted that FIGS. 5 and 6 illustrate the condenser microphone in which a microphone unit is removed from a condenser microphone body.
The illustrated condenser microphone 50 includes a microphone unit 52 and a microphone body 51. The microphone unit 52 converts sound waves to audio signals. The microphone body 51 accommodates a circuit portion for processing the audio signals received from the microphone unit 52, and the like. The microphone unit 52 is removably mounted, for example threadedly engaged, to the microphone body 51.
The microphone body 51 has a hollow cylindrical casing 53 for shielding static electricity. The casing 53 accommodates the circuit portion 54, a connector 55, and the like.
Further, the microphone unit 52 has a head case 65 formed with a large number of openings, and the head case 65 accommodates a unit body 56 including a fixed electrode and a diaphragm. Further, the microphone unit 52 has a pin input terminal 57, and a signal output terminal 59. The pin input terminal 57 is connected to the fixed electrode of the unit body 56, and disposed in back of the unit body 56. The signal output terminal 59 is connected to the pin input terminal 57 through a coil spring 58.
Further, a connection terminal 60 is provided in a front end opening of the microphone body 51 to receive abutment of a front end of the signal output terminal 59. The connection terminal 60 is connected to the circuit portion 54 side.
The microphone unit 52 is threadedly engaged with, for example, the front end opening of the casing 53 in the microphone body 51. As the result, the front end of the signal output terminal 59 is pressed against the connection terminal 60 by an urging force of the coil spring 58. Therefore, the unit body 56 and the circuit portion 54 are electrically connected, and the microphone unit 52 functions as a microphone.
Further, the condenser microphone 50 configured as described above may have a common specification of a coupled portion between the microphone unit 52 and the microphone body 51. The common specification allows interchange of only the microphone units 52 having different directivities. Accordingly, a variable directivity microphone having the common microphone body 51 can be readily achieved.
With the condenser microphone 50 having the above-mentioned configuration, a charged human body (150 to 200 pF) may make contact with the signal output terminal 59 during mounting and dismounting of the microphone unit 52. At this time, a static voltage (3 kV to 10 kV) is applied between the diaphragm and the fixed electrode. Therefore, this causes a problem in that the diaphragm is attracted to the fixed electrode, and the diaphragm is likely to be broken.
While, an omnidirectional unit employs stiffness control, and has a highly stretched diaphragm. Therefore, the problem of attraction of the diaphragm to the fixed electrode is reduced. However, a high voltage applied between the diaphragm and the fixed electrode causes a problem in that spark discharge occurs and the diaphragm is broken.
Further, with an electret condenser microphone unit, even if a diaphragm is not broken, electret may have a reduced surface potential. As a result, this causes a problem of deterioration in sensitivity of the electret condenser microphone unit.